In the construction of the buildings and the like from prefabricated concrete bodies constituted as blocks, panels or the like, it is standard practice to embed in such bodies so-called pickup bolts whose shafts are embedded in the body and extend slightly therefrom and which have heads on the ends of the shafts that are engaged by special pickup units for lifting of the body. In order to facilitate shipping of such a concrete body it is standard practice to recess the head of the bolt somewhat by forming the surface of the body at the bolt with an outwardly concave seat.
The standard pickup unit is a one-piece device formed as a so-called spoon, that is having a hollow head formed with an angularly extending slot one end of which is widened for fitting-in of the bolt head. This body has a radially extending arm that normally projects away from the head adjacent the wide end of the slot and lying in the plane of the slot. The free end of this arm is connected to the lift or hoist cable that in turn extends up to the boom of the crane.
In use such a device must be manhandled into position over the bolt to which it has to be connected, with sufficient slack in the lifting cable or rope to allow the arm to be laid practically flat down on the body to be lifted so that the wide end of the slot can be positioned over the bolt. After such positioning the entire assembly, including the length of cable connected to it, must be swung through a substantial angle to ensure that the bolt head is positioned well in the slot. Once the lift is done, the device must be pivoted back down to align the bolt with the wide end of the slot and then lifted off by hand.
Such an arrangement has several considerable disadvantages. First of all the necessity of positioning the entire unit by hand, including placing it over the bolt and removing it from over the bolt after the lift is completed, is extremely laborious. What is more the real danger exists in such a system that the arm will fall back to the position with the wide end of the slot over the bolt so that when the lift is attempted the pickup unit will merely be pulled off the body of concrete and will have to be repositioned. Finally it is impossible to actuate such a device from afar, even a relatively skillful crane operator can rarely succeed intentionally in lifting such a pickup unit off the body after a lift is completed.